Generally, an electronic control unit for automobiles is composed of a microcomputer and an output driver circuit. The microcomputer drives the output driver circuit so as to obtain an optimal driving state and controls various actuators on the basis of input signals from various sensors.
In this case, a power transistor such as a power MOSFET is used for the output driver circuit. A gate terminal is turned on or off according to a drive signal from the microcomputer and a desired current is supplied to the load of the actuator connected to a drain terminal. The drive signal from the microcomputer depends on the actuator and for example, in an electronic control unit for an engine, a pulse width modulation (PWM) signal for a valve switching solenoid, a pulse signal synchronized with engine rotation for an injector or an igniter, and a high or low signal according to on or off for a relay switch are general.
In recent years, a driver IC that power MOSFETs are integrated in correspondence to a plurality of channels and moreover serial communication interfaces are formed in one chip has been used for the output driver circuit. By use of such a driver IC, an on-off signal for driving a relay switch can be transmitted to the driver IC from the microcomputer via a serial communication line. A PWM signal and a pulse signal are individually generated for each actuator by a timer module built in the microcomputer and these signals are individually transmitted to the driver IC.
However, in a system that a PWM signal and a pulse signal are individually transmitted from the microcomputer for each actuator, a problem arises that many wires are required between the microcomputer and the driver IC. When the number of wires is increased, the circuit substrate area is increased and the miniaturization of the electronic control unit is restricted. Further, since the number of timer ports of the microcomputer is increased, another problem arises that the cost of the microcomputer package is increased.
Therefore, for example, as disclosed in Japanese Laid-open Patent Publication No. Hei 09-154181, it is known that an operation means 301 and a drive means 302 are connected by an interface means 103, thus the number of wires between the operation means 301 and the drive means 302 can be reduced. Further, in this example, it is unknown whether the operation means 301 and the drive means 302 are arranged in the same electronic control unit or not.